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Onboard systems intended to keep airliners from colliding in midair have been triggered more than 45 times this year in the skies over Washington as air traffic controllers have made dangerous mistakes at a record-setting pace.

With 38 officially reported errors this year, the controllers who guide planes to and from the region's airports already have exceeded annual error totals for every year since their facility began operation in 2003. The Federal Aviation Administration dispatched a safety review team to the Warrenton facility last month after a controller error resulted in a United Airlines flight narrowly missing a collision with a 22-seat Gulfstream business jet. One of the United passengers, Rep. F. James Sensenbrenner Jr. (R-Wis.), contacted the FAA.

The review team found that "more than 45 such events have been documented this calendar year" in which the avoidance alert systems have been triggered in the airspace controlled by the Potomac Terminal Radar Approach Control (TRACON), according to an internal FAA summary.

"Onboard collision avoidance systems give aircraft an extra margin of safety," Sasha J. Johnson, an FAA spokeswoman, said Monday. "However, the alert does not always mean that there was a loss of required separation between aircraft or that an unsafe situation exists."

Sensenbrenner's airliner came within 15 seconds of colliding with the smaller jet before onboard warning systems ordered the pilots to take evasive action, according to FAA documents. The pilot of the larger jet reported seeing the smaller plane pass just behind him, and according to an air traffic recording, he said, "That was close."

Two of the closest calls this month involved four airplanes, carrying a total of 589 people, and included one incident in which a Delta 737 was turned into the potentially deadly turbulent wake of a United 757 as the two planes flew along the Potomac River on final approach to Reagan National Airport.

Although few of those events were as harrowing as Sensenbrenner's experience, the review team said the controllers, who guide as many as 2,000 planes in the region each day, were being instructed to allow additional space between airplanes in TRACON airspace. The onboard systems, required on all planes carrying 19 or more passengers, kick in and order pilots to take evasive action when their sensors indicate a potential midair collision.

The Sensenbrenner incident on June 28 was recorded as the 23rd error of the year by Potomac TRACON. Since that date, controllers there officially have reported 15 more mistakes, including two this month that were ranked in preliminary internal reports as "category A, yellow." Only a "category A, red" is considered more serious, usually involving an actual crash or act of terrorism.

The first incident involved the two planes on approach to National. In the second, a preliminary report said that a controller jumbled the call signs of two planes approaching Dulles International Airport and directed a United Airlines 757 into the path of a United Express Saab 340. A later report assigned blame to the 757 pilot as well.

TRACON controllers take over once planes are airborne and guide them until they reach cruising altitude, where another group of controllers takes charge for the long haul. TRACON also directs inbound planes, releasing them to the tower when they are within seven miles of landing.

Among the more than 30 issues raised in the report by the "quality control" team was concern that TRACON controllers and tower controllers at Dulles were not playing by the same set of rules, with TRACON using the official playbook as a flexible guideline while Dulles used it as a mandate from which they "should only rarely deviate." The playbook establishes 14 approaches for managing arrivals and departures at the airport.